1. Field of the Invention
The present invention relates to a converter. More particularly, the present invention relates to a burst mode converter and a driving method thereof.
2. Description of the Related Art
A burst mode is a driving mode for a converter to output power through switching for a predetermined time, stop the switching for another predetermined time, and repeat the process so as to reduce power consumption when a load connected to the converter is low.
The conventional hysteretic burst mode converter has a simple structure, but it generates audible noise. The hysteretic burst mode converter uses a hysteresis comparator. In the case of using the hysteresis comparator, a group frequency is reduced in the burst mode. The group frequency represents a frequency corresponding to a group period. The group period is defined as the period which includes the period for outputting power through switching in the burst mode and the period for stopping the switching.
FIG. 1 shows a control signal (Vg) for determining an on/off of a main switch generated by a load connected to an output terminal of the conventional converter. The converter controls output power by using the main switch's on/off operation. The group frequencies of the control signal (Vgate) are indicated on the right hand side of FIG. 1, for respective loads. The respective load values are indicated on the left-hand side of FIG. 1. The control signal's time evolution illustrate the period of the switching operation. The direction of the arrow indicates on the left hand side indicates decreasing loads and increasing load currents. As shown in FIG. 1, the group frequency increases as the load is reduced. The group frequency bandwidth (1 Khz-14 Khz) is in the audible frequency bandwidth, generating inconvenience to a user because of the noise that is generated when the converter is operated.
Also, as the group frequency is reduced, a ripple of an output voltage of the converter is increased.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.